Conductor winding and inductors arranged to form a balun having a figure eight shape

ABSTRACT

A balun including a first conductor winding, a first inductor, a second inductor, a third inductor, and a fourth inductor. The first conductor winding has a figure eight shape including a first loop and a second loop. The first inductor and the second inductor substantially surround the first loop. The third inductor and the fourth inductor substantially surround the second loop.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present disclosure is a continuation of U.S. patent application Ser.No. 13/846,183 (now U.S. Pat. No. 8,791,769), filed on Mar. 18, 2013,which is a continuation of U.S. patent application Ser. No. 13/332,200(now U.S. Pat. No. 8,400,232), filed on Dec. 20, 2011, which claims thebenefit of U.S. Provisional Application No. 61/426,969, filed on Dec.23, 2010. The entire disclosures of the applications referenced aboveare incorporated herein by reference.

BACKGROUND

Unless otherwise indicated herein, the approaches described in thebackground section of the instant application are not prior art to theclaims in the application and are not admitted to be prior art byinclusion in the background section.

Baluns are electrical transformers that convert electrical signals thatare balanced about ground to electrical signals that are unbalancedabout ground. Baluns may also convert electrical signals that areunbalanced about ground and convert the electrical signals to beingbalanced about ground.

A balun typically includes two inductors where each inductor is formedfrom a set of wound conductors. The sets of wound conductors areinductively coupled if current is passed through one set of woundconductors. FIG. 1 is a simplified schematic of a traditional balun 100.Balun 100 includes a first set of wound conductors 105 and a second setof wound conductors 110. One wound conductor from each set of woundconductors 105 and 110 is shown in FIG. 1 for simplification. Each woundconductor in the set of wound conductors 105 may be adjacent to a woundconductor in the set of wound conductors 110. Traditional balunstypically tend to introduce a relatively large amount of cross talk(i.e., interference) with nearby circuits, such as other inductors,other baluns, and the like.

Therefore, it would be desirable to provide new baluns having relativelylower cross talk than traditional baluns and having smaller areas thantraditional baluns while providing the same efficiency.

SUMMARY

Embodiments described herein generally relate to baluns, and moreparticularly relate to a balun having a figure 8 shape, which providefor equivalent power transfer compared to a traditional balun andprovides such power transfer in relatively less area than a traditionalbalun.

According to one embodiment, a balun includes a first set of woundconductors includes a first loop portion and a second loop portion. Thefirst loop portion and the second loop portion are conductively coupledand form a first figure eight structure. The balun further includes asecond set of wound conductors includes a third loop portion and afourth loop portion. The third loop portion and the fourth loop portionare conductively coupled and form a second figure eight structure. Thefirst loop portion and the third loop portion are inductively coupled.The second loop portion and the fourth loop portion are inductivelycoupled.

According to a specific embodiment, the first set of wound conductorsincludes a set of conductive cross portions disposed between the firstloop portion and the second loop portion and conductively links thefirst loop portion and the second loop portion.

According to another specific embodiment, the second set of woundconductors includes another set of conductive cross portions disposedbetween the third loop portion and the fourth loop portion andconductively links the third loop portion and the fourth loop portion.

According to another specific embodiment, the first set of woundconductors includes a set of conductive un-crossing portions disposedbetween the first loop portion and the second loop portion andconductively links the first loop portion and the second loop portion.

According to another specific embodiment, the second set of woundconductors includes another set of conductive un-crossing portionsdisposed between the third loop portion and the fourth loop portion andconductively links the third loop portion and the fourth loop portion.

According to another specific embodiment, the first set of woundconductors are stacked above the second set of wound conductors.

According to another specific embodiment, the wound conductors of thefirst set of wound conductors are interleaved with the wound conductorsof the second set of wound conductors.

According to another specific embodiment, the wound conductors of thefirst set of wound conductors are stacked and interleaved with the woundconductors of the second set of wound conductors.

According to another specific embodiment, a number of wound conductorsin the first set of wound conductors does not match a number of woundconductors in the second set of wound conductors.

According to another specific embodiment, the balun further includesanother balun disposed in the first and the third loop portions; andanother balun disposed in the send and the fourth loop portions.

According to another specific embodiment, the first, the second, thethird, and the fourth loop portions are substantially round.

According to another specific embodiment, the first, the second, thethird, and the fourth loop portions are substantially oval.

According to another specific embodiment, the first, the second, thethird, and the fourth loop portions are substantially rectangular.

According to another specific embodiment, the first, the second, thethird, and the fourth loop portions each include substantially linearportions. According to another embodiment, a balun method of operationincludes directing current in a first set of wound conductors forming afirst figure eight structure, and inducing a current in a second set ofwound conductors forming a second first eight from the current directedthrough the first set of wound conductors. The method further includesestablishing from the current directed through the first set of woundconductors a first magnetic field in a first loop portion of the firstfigure eight structure of the first set of wound conductors. The methodfurther includes establishing from the current directed through thefirst set of wound conductors a second magnetic field in a second loopportion of the first figure eight structure of the first set of woundconductors; wherein the first magnetic field and the second magneticfield are oppositely directed.

According to a specific embodiment, the method further includescanceling portions of the first magnetic field with portions of thesecond magnetic field outside of the first set of wound conductors.

According to a specific embodiment, the method further includesestablishing from the induced current directed through the second set ofwound conductors a third magnetic field in a third loop portion of thesecond figure eight structure of the second set of wound conductors. Themethod further includes establishing from the induced current directedthrough the second set of wound conductors a fourth magnetic field in athird loop portion of the second figure eight structure of the secondset of wound conductors. Third magnetic field and the fourth magneticfield are oppositely directed.

According to a specific embodiment, the method further includescanceling portions of the third magnetic field with portions of thefourth magnetic field outside of the second set of wound conductors.

According to a specific embodiment, the method further includesinhibiting cross talk with adjacent circuit structures via the firstcancellation step and the second cancellation step.

According to another embodiment, a fully-differential power amplifierincludes a first power amplifier core including first and secondinductors having an output AC signal directed across the first and thesecond inductors, and a second power amplifier core including third andfourth inductors having the output AC signal directed across the thirdand the fourth inductors. The fully-differential power amplifier furtherincludes a balun including a set of wound conductors having a first loopportion and a second loop portion conductive coupled to the first loopportion. The first loop portion and the second loop portion form afigure eight structure. The first loop portion is configured toinductively couple the first and the second inductors to the balun. Thesecond loop portion is configured to inductively couple the third andthe forth inductors to the balun.

According to a specific embodiment, the fully-differential poweramplifier further includes an antenna coupled to the balun andconfigured to receive the AC signal from the balun for transmission. Thefully-differential power amplifier may also include an antenna coupledto the balun and configured to receive the AC signal from the balun fortransmission.

The following detailed description and accompanying drawings provide amore detailed understanding of the nature and advantages of the presentinvention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a simplified schematic of a traditional balun;

FIG. 2A is a simplified schematic of a balun according to oneembodiment;

FIG. 2B is a simplified schematic of magnetic fields established by afirst loop and a second loop of the first set of wound conductors wherethe magnetic fields in the first and the second loops are in oppositedirections;

FIG. 3A is a simplified schematic of a balun according to an alternativeembodiment where loops of the balun are substantially oval;

FIG. 3B is a simplified schematic of a balun according to an alternativeembodiment where loops of the balun are substantially rectangular;

FIG. 3C is a simplified schematic of a balun according to anotheralternative embodiment where one set of loops of the balun havesubstantially straight lines portions and along an extended axis of thebalun;

FIG. 4 is a simplified schematic of a fully-differential power amplifierin which balun embodiments described herein is configured for use in acoupler for coupling an AC output of the fully-differential amplifier toan antenna;

FIG. 5 is a simplified schematic of a balun configured to inductivelycouple output AC signals of a fully-differential power amplifier, suchas that shown in FIG. 5, to an antenna according to one embodiment;

FIG. 6 is a simplified schematic of balun where inductors substantiallysurround portions of the first loop and the second loop of the balun toreduce mechanical forces on the balun due to the interacting magneticfields of the balun; and

FIG. 7 is a simplified schematic of balun according to anotherembodiment.

DESCRIPTION

Embodiments described herein generally provide to baluns, and moreparticularly provide a balun having a FIG. 8 shape, which provide forequivalent power transfer compared to a traditional balun and providessuch power transfer in relatively less area than a traditional balun.

In the following description, for purposes of explanation, numerousexamples and specific details are set forth in order to provide athorough understanding of embodiments of the present invention.Particular embodiments as defined by the claims may include some or allof the features in these examples alone or in combination with otherfeatures described below, and may further include modifications andequivalents of the features and concepts described herein.

FIG. 2A is a simplified schematic of a balun 200 according to oneembodiment. Balun 200 includes a first set of wound conductors 205 and asecond set of wound conductors 210. For simplicity, one wound conductor205 a (shown as a solid line in FIG. 2A) from the first set of woundconductors 205 is shown in FIG. 2A, and one wound conductor 210 a (shownas a dashed line in FIG. 2A) from the second set of wound conductors 210is shown in FIG. 2A. The first set of wound conductors 205 may includean input node 215 and an output node 220. The second set of woundconductors 210 may include an input node 225 and an output node 230.

The following description of balun 200 describes wound conductor 205 aincluded in the set of wound conductors 205 and describes woundconductor 210 a included in the set of wound conductors 210. Thefollowing description of wound conductor 205 a and wound conductor 210 amay apply to each of the wound conductors included the sets of woundconductors 205 and 210. Specifically, wound conductor 205 a may includea first loop 205 b conductively coupled to a second loop 205 c where thefirst loop 205 b and the second loop 205 c are adjacent. First loop 205b and second loop 205 c may cross over each other in a central portion205 d of wound conductor 205 a. Thereby, first loop 205 b and secondloop 205 c may form substantially a “figure eight” structure. Woundconductor 210 a may similarly include a first loop 210 b conductivelycoupled to a second loop 210 c. First loop 210 b and second loop 210 cmay cross over each other in a central portion 210 d of wound conductor210 a. Thereby, first loop 210 b and second loop 210 c may formsubstantially a “figure eight” structure. The central portions 205 d and210 d may be laterally offset so that the crossing portions of the woundconductor 205 a and 210 a shown in FIG. 2A may cross at differentlocations. The crossing portions of the wound conductor 205 a and 210 amay be stacked or interleaved according to alternative embodiments.According to an alternative embodiment, the centrals portion 205 d ofthe first loop 205 b and second loop 205 c do not cross, and the centralportion 210 d of the first loop 210 b and the second loop 210 c do notcross.

For convenience, first loop 205 b is shown in FIG. 2A as being outsideof first loop 210 b, and second loop 205 c is shown as being outside ofsecond loop 210 c. The first loops 205 b and 210 b, and the second loops205 c and 210 c may be alternatively configured with first loop 205 boverlying first loop 210 b and second loop 205 c overlying second loop210 c.

According to one embodiment, the set of wound conductors 205 are stackedabove the set of wound conductors 210. Stacked sets of wound conductors205 and 210 provide relatively low insertion loss and relatively highinductive coupling. According to an alternative embodiment, the woundconductors of the set of wound conductors 205 and the wound conductorsof the set of wound conductors 210 interleave one another. Interleavedwound conductors provide relatively low secondary resonances due to thecapacitance provided by the parasitic capacitance between the sets ofwound conductors. Secondary resonances are lower order harmonics andhigher order harmonics of the fundamental harmonic (i.e., fundamentalfrequency) of an AC signal received by balun 200. Stacked sets of woundconductors 205 and 210 may have relatively higher secondary resonancesacross cross capacitor 260 at relatively high frequencies. According toone embodiment, the sets of wound conductors 205 and 210 are bothstacked and interleaved. Stacking and interleaving the sets of woundconductors 205 and 210 provides for a tradeoff between insertion lossesand the generation of secondary resonances.

FIG. 2B is a simplified schematic of magnetic fields established byfirst loop 205 b and second loop 205 c wherein the magnetic fields inthe first and the second loops 205 b and 205 c are in oppositedirection. The first and the second loops 210 b and 210 c are not shownin FIG. 2B for convenience. For example, for a first direction ofcurrent flow in the set of wound conductors 205, the direction of themagnetic field in first loop 205 b may be out of the plane of the pageof FIG. 2B (conventionally designated with a dot inside a circle “⊙” asshown in FIG. 2B), and the direction of the magnetic field in secondloop 205 c may be into the plane of the page of FIG. 2 (conventionallydesignated with a cross inside a circle “{circle around (x)}” as shownin FIG. 2B). As will be understood by those of skill in the art, themagnetic fields extending outside of first loops 205 a and 210 a willalso be in the opposite direction of magnetic fields extending outsideof second loops 205 b and 210 b. Because the magnetic fields establishedby first loop 205 b is oppositely directed from the magnetic fieldsestablished by second loop 205 c, the magnetic fields extending frombalun 200 tend to cancel each other. The cancellation of the oppositelydirected magnetic fields provides that the magnetic fields have arelatively reduced potential for inducing cross talk (i.e.,interference) in adjacent circuits structures, such as inductors, otherbalun, and the like. For example, compared to a traditional balun, suchas balun 100 shown in FIG. 1, balun 200 may provide a gain ofapproximately 30 d B of isolation from an adjacent circuit structure,such as another balun. While FIG. 2B shows the magnetic fields for thefirst loop 205 b and the second loop 205 c, the magnetic fields forfirst loop 210 b and the second loop 210 c are similar, but oppositelydirected for the direction of current flow as shown in FIG. 2B.

Balun 200 further provides an inductance that matches the inductance ofa traditional balun while having a smaller area. For example, balun 200may provide an inductance that substantially matches the inductance of atraditional balun while having an area that is approximately 1.6 timesto 1.7 times less than the area of a traditional balun. Therefore, foran application such as an integrated circuit, balun 200 may consumeconsiderably less die area than a traditional balun.

While first loops 205 b and 210 b, and second loops 205 c and 210 c areshown in FIG. 2 as being substantially circular, the first loops andsecond loops of the sets of wound conductors 205 and 210 may bealternatively shaped according to alternative embodiments. FIG. 3A is asimplified schematic of a balun 250 according to an alternativeembodiment where first loops 205 b and 210 b, and second loops 205 c and210 c are substantially oval. FIG. 3B is a simplified schematic of abalun 260 according to an alternative embodiment where first loops 205 band 210 b, and second loops 205 c and 210 c are substantially oval. Itis noted that the elongated axes of the oval shaped loops shown in FIG.3A are rotated approximately ninety degrees from the elongated axes ofthe oval shaped loops shown in FIG. 3B. FIG. 3C is a simplifiedschematic of a balun 270 according to another alternative embodimentwhere first loops 205 b and 210 b, and second loops 205 c and 210 c havesubstantially straight lines portions 280 and 285 along an extended axis290 of balun 270. While balun 200 is described as including sets ofwound conductors 205 and 210 in a FIG. 8, alternative balun embodimentsmay include more sets of wound conductors coupled to the set of woundconductors 205 or the set of wound conductors 210. Such a balun may looklike three, four, or more sets of adjacent wound-conductor loops thatare conductive coupled. According to various embodiments describedherein, the number of wound conductors in the first set of woundconductors 205 may match the number of wound conductors in the secondset of wound conductors 210. Alternatively, the number of woundconductors in the first set of wound conductors 205 may be differentthan the number of wound conductors in the second set of woundconductors 210.

FIG. 4 is a simplified schematic of a fully-differential power amplifier500 inductively coupled to a coupler 505, which includes a set ofinductors 515. Coupled 505 may be configured to inductively coupled theoutput of the fully-differential power amplifier 500 to an antenna 510.Balun embodiments described herein may be configured for inclusion incoupler 505 and first-fully differential amplifier 500 for inductivelycoupling coupler 505 to fully-differential power amplifier 500 as willbe described in further detail below. Power amplifiers, such asfully-differential power amplifier 500, are generally configured toreceive an AC signal, such as an RF signal, and boost the power of thereceived AC signal. Fully-differential power amplifiers may be includedin a variety of mobile devices, such as mobile telephones, computers(such as laptop computers, tablet computers, etc.), personal digitalassistants, and the like. A power-amplified AC signal may be directedthrough an antenna of a mobile device for transmission.

Fully-differential power amplifier 500 includes a first power-amplifiercore 300 a (generally surrounded by a dashed line in FIG. 4) and asecond power-amplifier core 300 b (also generally surrounded by a dashedline in FIG. 4). The same numbering system used for identifying circuitelements of first power-amplifier core 300 a is used for identifying thesubstantially same circuit elements of second power-amplifier core 300 bwhere numbers used for second power-amplifier 300 b are primed. Thefirst and second power-amplifier cores 300 a and 300 b havesubstantially similar circuits and have substantially similar circuitlayouts. Therefore, the first power-amplifier core 300 a is described indetail, and the second power-amplifier core 300 b is not described. Thedescription of the first power-amplifier core 300 a applies the secondpower-amplifier core 300 b.

First power-amplifier core 300 a includes a push-pull pair oftransistors 305 and 310, (referred to as transistors 305 and 310). Firstpower-amplifier core 300 a further includes a transistor 405 disposedbetween transistor 305 and a first inductor 315, and includes atransistor 410 disposed between transistor 310 and a second inductor320. Transistors 405 and 410 are sometimes referred to herein as asecond push-pull pair of transistors.

Transistors 305 and 405 may be in a cascode configuration with a,respective, common source, common ground configuration. Morespecifically a source 405 b of transistor 405 may be coupled to thedrain 305 c of transistor 305, and a drain 405 c of transistor 405 maybe coupled to the first end of first inductor 315 where the second endof first inductor 315 is coupled to the voltage source Vdd. A gate 405 aof transistor 405 may be grounded or the like to relatively stronglyturn on transistor 405.

Transistors 310 and 410 may similarly be in a cascode configuration witha, respective, common source, common ground configuration. Morespecifically a source 410 b of transistor 410 may be coupled to thedrain 310 b of transistor 310, and a drain 410 c of transistor 410 maybe coupled to the first end of second inductor 320 where the second endof inductor 320 is coupled to ground. A gate 410 a of transistor 410 maybe grounded or the like to relatively strongly turn on transistor 410.The cascode configuration of the transistors provide for stressprotection of power amplifier 400 as will be well understood by those ofskill in the art. According to one embodiment, the gates 305 a and 310 aare first and second inputs 350 and 355 of fully-differential poweramplifier 500.

First power-amplifier core 300 a may also include first and second tankcapacitors 330 and 335. Capacitor 330 is coupled to inductor 315 inparallel (i.e., in a “tank” configuration). Tank capacitor 330 isconfigured to tune the resonant frequency of inductor 315. Tankcapacitor 335 is coupled to inductor 320 in a tank configuration. Tankcapacitor 335 is configured to tune the resonant frequency of inductor320.

Transistors 305, 310, 405, and 310 may be metal-oxide-semiconductorfield-effect transistors (MOSFETs), bipolar-junction transistors (BJTs),or other transistors types. According to one embodiment, transistors 305and 405 are nMOS transistors where transistor 405 has a drain 405 c(sometimes referred to a drain region) coupled to a first end ofinductor 315 where a second end of inductor 315 is coupled to a voltagesource Vdd. A first output node (Vout1) 347 a is disposed between drain405 c and the first end of inductor 315. A source 305 b of transistor305 may be coupled to a first end of a third inductor 340 where a secondend of the third inductor 340 is coupled to ground. Specificconfigurations of the sources and the drains of transistors 305, 310,405, and 410 are described herein for convenience of explanation ofspecific embodiments. Alternative embodiments of the power amplifiersmay include alternative configurations of the sources and drains oftransistors 305 and 310 as will be understood by those of skill in theart. As will be further understood by those of skill in the art, sourcesand drains are sometimes referred to herein as source-drain nodes.

According to one embodiment, transistors 310 and 410 are pMOStransistors where transistor 410 includes a drain 410 c coupled a firstend of inductor 320 where a second end of inductor 320 is coupled toground. A second output node (Vout2) 347 b is disposed between source410 c and the first end of inductor 320. A source 310 c of transistor310 is coupled a first end of a fourth inductor 345 where a second endof fourth inductor 345 is coupled to the voltage source Vdd. Inductors315 and 320 may be considered the respective loads of the push-pull pairof transistors 305 and 310.

As described briefly above, coupler 505, via the set of inductors 515,is configured to inductively couple an output AC signals acrossinductors 315, 320, 315′, and 320′ to antenna 510. For convenience,coupler 505 is shown as including the set of inductors 515 as asimplification for indicating the inductive coupling of the output ACsignal across inductors 315, 320, 315′, and 320′ to antenna 510. Asdescribed briefly above, balun embodiments described herein may beconfigured to inductively couple the AC output signals across inductors315, 320, 315′, and 320′ to antenna 510.

FIG. 5 is a simplified schematic of a balun 600 configured toinductively couple the output AC signals of fully-differential poweramplifier 500 to antenna 510 according to one embodiment. Balun 600includes the first set of wound conductors 205 where the first loop 205b is inductively coupled to inductors 315 and 320, and the second loop205 c is inductively coupled to inductors 315′ and 320′. Inductors 315and 320 may be curved to conform to the loop shape of the first loop 205b, and inductors 315′ and 320′ may be curved to conform to a loopedshape of the second loop 205 c such that inductors 315 and 320, 315′,and 320′ form a substantially figure eight shape similar to the figureeight shape of the first set of wound conductors 205. Balun 600 mayinclude inductors 315, 320, 315′, and 320′. The first set of woundconductors 205 may inductively coupled the AC output signal acrossinductors 315, 320, 315′, and 320′ to antenna 510 for transmission ofthe AC output signal.

According to one embodiment, inductors 315, 320, 315′, and 320′ may beshaped to substantially surround portions of the first loop 205 b andthe second loop 205 c. FIG. 6 is a simplified schematic of balun 700where inductors 315, 320, 315′, and 320′ substantially surround portionsof the first loop 205 b and the second loop 205 c.

FIG. 7 is a simplified schematic of balun 800 according to anotherembodiment. Balun 800 is substantially similar to balun 600 and balun700 described above, but differs in that balun 800 includes anadditional first balun 200 a and/or an additional second balun 200 bwhere baluns 200 a and 200 b may be disposed in the first loop 205 b andthe second loop 205 c. “Nesting” balun according to embodiments of thepresent invention may efficiently use space for these balun in anintegrated circuit or the like. Balun 200 a and 200 b may each be abalun 200 described above or may be other balun embodiments describedherein. Balun 200 a and 200 b may be configured for inductively couplingother circuit structures, such as a set of input inductors offully-differential power amplifier 500. While inductors 315′ and 320′are shown in FIGS. 5, 6, and 7 as being coupled to ground, according toalternative embodiments, inductors 315′ and 320′ may be coupled to an ACground.

The above description illustrates various embodiments of the presentinvention along with examples of how aspects of the present inventionmay be implemented. The above examples and embodiments should not bedeemed to be the only embodiments, and are presented to illustrate theflexibility and advantages of the present invention as defined by thefollowing claims. Based on the above disclosure and the followingclaims, other arrangements, embodiments, implementations, andequivalents may be employed without departing from the scope of theinvention as defined by the claims.

What is claimed is:
 1. A balun, comprising: a first conductor windinghaving a figure eight shape, wherein the figure eight shape of the firstconductor winding includes a first loop and a second loop; a firstinductor; a second inductor, wherein the first inductor and the secondinductor substantially surround the first loop; a third inductor; and afourth inductor, wherein the third inductor and the fourth inductorsubstantially surround the second loop.
 2. The balun of claim 1, whereinthe first inductor and the second inductor are curved to conform to ashape of the first loop.
 3. The balun of claim 1, wherein the thirdinductor and the fourth inductor are curved to conform to a shape of thesecond loop.
 4. The balun of claim 1, wherein the first inductor and thesecond inductor are inductively coupled to the first loop.
 5. The balunof claim 1, wherein the third inductor and the fourth inductor areinductively coupled to the second loop.
 6. The balun of claim 1, whereinthe first inductor and the second inductor are coupled to a supplyvoltage.
 7. The balun of claim 1, wherein the third inductor and thefourth inductor are coupled to ground.
 8. The balun of claim 1, wherein:the first loop and the second loop are not concentric.
 9. The balun ofclaim 1, wherein: the first loop and a third loop formed by the firstinductor and the second inductor are concentric.
 10. The balun of claim1, wherein: the second loop and a fourth loop formed by the thirdinductor and the fourth inductor are concentric.
 11. The balun of claim1, further comprising a second conductor winding having a figure eightshape, wherein the figure eight shape of the second conductor includes athird loop and a fourth loop each surrounded by i) the first loop, orii) the second loop.
 12. The balun of claim 1, wherein: the firstconductor winding includes a first input node and a first output node,wherein the first conductor winding is configured to receive current viathe first input node and output current via the first output node tocause i) a first magnetic field to flow in a first direction in thefirst loop, and ii) a second magnetic field to flow in a seconddirection in the second loop.
 13. The balun of claim 1, wherein thefirst loop and the second loop are substantially round, substantiallyoval, or substantially rectangular.
 14. A power amplifier comprising thebalun of claim
 1. 15. The power amplifier of claim 14, furthercomprising an antenna configured to receive an AC signal from the balun.16. A cellular phone comprising the power amplifier of claim 14.